Hydrogen storage in polymer-functionalized Pd-decorated single wall carbon nanotubes.

Palladium is usually supported on porous materials in the form of nanoparticles. The hydrogen storage capacity of such a system is usually much higher than the separated capacity of the metal (approximately 0.7 H/Pd) and the support. Pd nanoparticles provide a source of hydrogen atoms by dissociation. The atomic hydrogen spills over from the Pd structure to the support via surface diffusion and this phenomenon is known as hydrogen spillover. In this study commercial SWNTs were dispersed in PEG 200 solution. Then the precursor PdCl2 in PEG 200 was added and the whole left to react under stirring with reflux at 200 degrees C for 1 h. Succeeding washings with ethanol and centrifugation followed for several times and finally the sample was dried at 60 degrees C. Through this procedure a 3 wt% Pd loading was achieved whereas the TEM derived nanoparticle size distribution indicated a 50% percentage of Pd nanoparticles with diameter less than 8 nm. Hydrogen isotherms up to 2 MPa were carried out with the gravimetric method. The defined storage capacity of 1.2 wt% at 0.2 MPa was quite satisfactory. However, a 0.2 wt% portion of this storage capacity was attributed to the formation of water molecules through reaction of H atoms with the dissociatively adsorbed oxygen atoms on the Pd nanoparticles. This conclusion was educed from a series of thermal desorption experiments following the H2 adsorption/desorption cycles and regeneration. Through this set of experiments several other important parameters were defined as the temperature for complete hydrogen desorption and the optimum conditions for PEG removal.

Prediction of binary adsorption isotherms of Cu(2+), Cd(2+) and Pb(2+) on calcium alginate beads from single adsorption data.

The binary adsorption of Cu(2+)-Cd(2+), Pb(2+)-Cd(2+) and Pb(2+)-Cu(2+) mixtures onto Ca-Alginate beads, prepared from Laminaria digitata, was studied using batch experiments. Competitive sorption models including extended Sips, extended Langmuir, Jain and Snoeyink modified Langmuir (JS modified) as well as Ideal Adsorpted Solution Theory (IAST) models were applied to predict the binary adsorption using single component adsorption parameters. The extended and the JS modified Langmuir approaches provide excellent prediction of the binary adsorption, while the extended Sips fails to predict the experimental data, giving only fair results in the case on Pb(2+)-Cu(2+) mixtures. On the contrary, the IAST models, though they are more complicated, provide less accurate estimation of sorption in binary metal ion solutions. In general, single component adsorption parameters can be effectively used for the prediction of a materials adsorption performance in binary metal ion solutions.

Aqueous and gaseous adsorption from montmorillonite-carbon composites and from derived carbons.

Clay-carbon composites and the carbons derived from demineralization of the clay template were examined for their aqueous adsorption properties (2,4,6-trichlorophenol and methylene blue) and for their gas adsorption/separation abilities regarding CO(2), CH(4), and N(2) gases. The sorption results are discussed in relation with their structural properties (surface area, pore width and volume, and surface chemistry). It was found that the properties of the adsorbents depend highly on the synthetic route, for instance, on the use of clay or H(2)SO(4) as structure mediating and activating agents, respectively. Particularly, the simultaneous use of clay and H(2)SO(4) leads to a synergistic action, which imparts to the final solids the highest sorption capacity and the best potential for separation of CO(2) from gaseous mixtures of CH(4) and N(2).